Distillate fuels which are intended for use in internal combustion engines or jet turbines must meet certain minimum standards in order to be suitable for use. Diesel and jet fuel must have good oxidation stability in order to prevent the formation of unacceptable amounts of deposits which are harmful to the engines in which they are intended to be used. Distillates having very high levels of saturates, such as distillates recovered from the Fischer Tropsch process, have been shown to have excellent cetane numbers and low sulfur contents. Highly paraffinic distillates, as such, appear to be useful for blending with lower quality distillates, such as those with high aromatic contents, to obtain a distillate blend meeting the requirements for its intended application, whether as diesel fuel or jet fuel.
In general, two classes of oxidation stability are of concern in this disclosure. The first is the result of low sulfur levels in the distillate, such as found in Fischer Tropsch distillates and fuels which have been hydrotreated to low sulfur levels. Such hydrocarbons are known to form peroxides which are undesirable because they tend to attack the fuel system elastomers, such as are found in O-rings, hoses, etc. The second source of concern is in the formation of solid deposits as a result of the blending of the different components. For example, it has been found that highly paraffinic distillates, such as Fischer Tropsch products, when blended with highly aromatic petroleum-derived distillates, such as FCC light cycle oil, will result in an unstable blend which forms an unacceptable amount of solid deposits. When a blend of at least two distillate fuel components in some blending proportions result in the formation of unacceptable amounts of deposits as measured by ASTM D6468, the components are described as having “antagonistic properties”.
In the case of peroxide formation, it has been suggested that the formation of peroxides in the blends may be controlled by increasing the sulfur content of the blend. See WO 00/11116 and WO 00/11117 which describe the addition of at least 1 ppm sulfur to the blend in order to prevent sulfur formation. This approach has two drawbacks. The first is that this approach does not address the problem associated with the antagonistic properties of the blending components. The second problem is that sulfur in fuels is considered an environmental hazard and it is desirable to reduce the level of sulfur in fuels not increase it.
The present invention is directed to a process for blending highly paraffinic distillate fuel components and petroleum-derived distillate fuel components having high aromatics, the two components having antagonistic properties at certain ratios which result in the formation of unacceptable amounts of solid deposits. The process of the invention also may also be used to reduce the formation of peroxides in the blend without the addition of sulfur. The invention also results in a unique product blend which is suitable for use in internal combustion engines.